The oxidation reaction commonly used for preparing dihydroperoxides such as para-diisopropylbenzene dihydroperoxide includes oxidation of the para-dialkylaromatic with molecular oxygen in the presence of an aqueous alkaline material at increased pressure and temperature. In preparing the dihydroperoxides by such an oxidation reaction, it is the practice to continue the reaction only partially to completion (based upon the total dialkylbenzene present) since as the oxidation reaction is carried further toward completion, an even increasing amount of the dialkylbenzene is connected to undesireable oxidation products, such as carboxylic acids and ketones. Thus, since the oxidation reaction is carried only to partial completion, large amount of monohydroperoxide, the dihydroperoxide intermediate, as well as unreacted dialkylbenzene are present in the oxidation reaction mixture.
The oxidation reaction to produce dihydroperoxides from para-dialkylaromatic hydrocarbons is inhibited by certain materials such as phenolics which may occur in the dialkylbenzene feed to the oxidation reaction. Also, acidic materials such as carboxylic acids may cause rearrangement of the hydroperoxides formed in the oxidation reaction, to phenolics, thereby inhibiting the oxidation reaction. It is known to treat the dialkylbenzene feed to the oxidation reaction with strong aqueous solutions of alkali metal hydroxides whereby the unwanted inhibitor compounds will react to form water soluble salts of the phenolics and carboxylic acids, which may be then separated from the dialkylbenzene. Such a treatment process requires a special dialkylbenzene treatment facility and requires an excess amount of alkali metal hydroxide to ensure the complete removal of such inhibitors. The para-dialkylaromatic dihydroperoxides are conveniently recovered from the oxidation reaction mixture by a crystallization technique. However, significant amounts of the mono-hydroperoxide and unreacted dialkylbenzene are retained in the solid dihydroperoxide product. It is desirable to separate the monohydroperoxide and the dialkylbenzene from the dihydroperoxide to achieve improved quality of the latter product as well as to recover the valuable precursors for recycle to the oxidation reaction. In a continuous reaction to produce dihydroperoxide from dialkylbenzenes employing a recycle stream comprising monohydroperoxide and unreacted dialkylbenzene, care must be taken to prevent the increase in concentration of unwanted reaction by-products, particularly carboxylic acids. These by-products, unless removed from the reation system, will increase in concentration until they begin to interfere with the oxidation reaction. Where an aqueous alkaline material is employed within the oxidation reaction, substantial amount of by-products such as carboxylic acids and phenolic materials will react to form their sodium salts which are soluble in the aqueous phase. Good separation of the aqueous phase from the organic reaction product will ensure that these by-prodoucts will be removed as they are formed. Other oxidation by-products, comprising such compounds as alpha, alpha' -dihydroxy dialkyl benzene and alpha hydroxy - alpha' hydroperoxy dialkylbenzene tend to crystalize along with the dihydroperoxides whereby they are conveniently removed from the oxidation system. These by-products, if allowed to increase in the oxidation reaction system, will adversely affect the oxidation by their dilution effect. Additionally, they are further oxidized to such unwanted by-products as carboxylic acids and acetophenone-type compounds. These by-products, as they crystallize with the dihydroperoxides, are conveniently removed from the oxidation system with the dihydroperoxides. The dihydroperoxides containing these by-products may be utilized, for instance in the production of dihydric phenols by acid catalyzed rearrangement, or the dihydroperoxides may be further purified to remove such by-products.
The oxidation reaction products remaining after the para-dialkylaromatic dihydroperoxide is recovered comprise unreacted para-dialkylaromatic hydrocarbon and para-dialkylaromatic monohydroperoxide, both of which are precursors of the para-dialkylaromatic dihydroperoxide. The prior art teaches that these materials may be recycled to the oxidation reaction for conversion into additional amounts of para-dialkylbenzene dihydroperoxide.